Exercise, whatever form you can

I can't say I had "good form" when I did about 75 percent of a roller derby tryout for a news story on the Dallas Derby Devils late last year.
But what I did find that I had was a lot of muscle memory.
Although I hadn't been running ever since the inaugural San Antonio Rock 'n' Roll Marathon, where I ran the half, getting tossed around with the roller girls didn't result in a lot of leg pain. Although it did take at least three months for my right shoulder to stop hurting...
Rollerskating is a really good cardio sport. I personally prefer the quad skates because I can balance easier.
When the weather outside is miserable, go to the skating rink. As it was in high school, going skating is still pretty cheap, and for me, skating the track for two hours felt a lot like running a 10K.